1. Field of the Invention
The present invention relates to a transmission system with an overrunning clutch capable of allowing overrunning rotation on an output side.
2. Description of the Related Art
Conventionally, a transmission system of this type is constructed such that an overrunning clutch is interposed between an input shaft and an output shaft, whereby a torque from an input shaft side is transmitted to an output shaft side via the overrunning clutch, whereas a reverse driving torque is prevented from being transmitted from the output shaft side to the input shaft side through the action of the overrunning clutch.
Note that there are two types of overrunning clutch; a one-way clutch which acts only in one direction, and a two-way clutch which allows the overrunning rotation of the output member in a clockwise direction when the input member rotates in the clockwise direction and allows the overrunning rotation of the output member in a counterclockwise direction when the input member rotates in the counterclockwise direction.
Since the durability of an overrunning clutch is damaged when an excessive torque acts thereon, in a transmission system for transmitting a large magnitude of torque, a special overrunning clutch having a large torque transmission capacity needs to be used, and this surely increases costs.
The present invention was made in view of the above drawback, and an object thereof is to provide a transmission with an overrunning clutch capable of transmitting a large magnitude of torque even if it is provided with only a small torque transmission capacity.
With a view to attaining the above object, according to the present invention, there is provided a transmission system with an overrunning clutch capable of allowing overrunning rotation on an output side comprising a main clutch comprising in turn a mechanical friction clutch interposed between an input shaft and an output shaft of the transmission system and a pilot clutch comprising in turn a normally engaged friction clutch interposed between an output member of the overrunning clutch and the output shaft, wherein an input member of the overrunning clutch is allowed to freely rotate relative to the input shaft, and wherein a cam mechanism is coupled to the input member which is adapted to generate a thrust force to bring the main clutch into engagement by virtue of the difference in rotational speed between the input shaft and the input member.
When a load is acting on the output shaft, a loading torque equal to the torque transmission capacity of the pilot clutch is transmitted to the input member of the overrunning clutch via the pilot clutch and the overrunning clutch. When the input shaft is rotated in this state, there is generated a difference in rotational speed between the input shaft and the input member, and the main clutch is brought into engagement with the input member. Thus, even if the torque transmission capacity of the overrunning clutch is small, a large magnitude of torque can be transmitted from the input shaft to the output shaft via the main clutch.
In addition, when the rotation of the output shaft overruns that of the input shaft, since the loading torque is prevented from being transmitted to the input member of the overrunning clutch by virtue of the action of the overrunning clutch, the cam mechanism no more generates the thrust force and this releases the main clutch, whereby the reverse torque is prevented from being transmitted from the output shaft side to the input shaft side.